The human cost in terms of death and suffering, from the Japanese earthquake and tsunami of March 11, 2011, was immense. The death toll was over 15,900, with an additional 2,600 missing and presumed dead. In addition, 340,000 people were displaced from their homes.

The recovery effort continues but there is a long way to go, and many people are still not able to return to their normal lives—yet another form of suffering. The large numbers of displaced people present a huge public health challenge for the Japanese government with no clear end in sight. On top of that, radioactivity that was released from the compromised nuclear reactors at the Fukushima Daiichi power plant continues to thwart efforts to achieve full recovery. The local environment is still contaminated with radioactivity, and radioactivity stored on the plant grounds still threatens to taint groundwater.

Now that the aftermath of the earthquake and tsunami has run its course, people are anxious to return home and resume their lives. But a major concern is whether it is safe to return to areas with radioactive contamination, particularly in light of the reality that radiation levels will not be soon returning to the low background levels that existed prior to the accident.

The Japanese government has set a radiation mitigation goal of 20 mSv per year as the maximum annual dose allowable for returning evacuees. Prior to the accident, 1 mSv per year had been the dose limit for the public—a limit that is no longer sustainable if the region is ever to be reinhabited. The Fukushima evacuees now need to decide for themselves whether the government’s new 20 mSv per year dose limit presents a personal risk level that is acceptable. It is an important decision because, one way or another, how they decide will have a huge impact on how the rest of their lives unfold.

CC image courtesy of greensefa on flickr

As I describe in my book, Strange Glow: The Story of Radiation, we have over a century of experience with human exposures to man-made radiation, and that experience has taught us much about the health risks at various radiation dose levels. These data on human exposures suggest that 20 mSv of dose represents a lifetime risk of a fatal cancer of about 1 in 1,000. Stated another way, if 1,000 people lived in a radiation-contaminated area for one year and received this level of dose during their stay, we might expect one of them to come down with a fatal cancer at some point in their remaining lifetime due to that radiation exposure. Meanwhile, as many as 250 of those same 1,000 people would be expected to sustain a fatal cancer as some point during their life from non-radiation causes because, unfortunately, cancer is a common disease.

So compared to people living elsewhere in Japan, the cancer rate for the returning Fukushima residents would raise from a baseline of 250 out of 1,000, up to 251 out of 1,000, during their first year of rehabitation. Each additional year of residence at 20 mSv per year would increase the lifetime cancer risk level by one additional victim per 1,000. So two years of 20-mSv exposure would result in 252 cancers out of 1,000, compared to the 250 out of 1,000 risk level in uncontaminated areas.

It must be understood that these numbers are just approximations of the cancer risks. But they are good approximations backed up by a century of health experience with human radiation exposures, including atomic bomb victims, nuclear fallout victims, and people exposed to medical radiation procedures. They may not be very precise estimates, but they are definitely in the ballpark for the true level of cancer risk from radiation.

CC image courtesy of thlerry ehrmann

Now, knowing the risk of cancer associated with returning, what are the risks of not returning. Well, that will depend more upon the exact personal circumstances of affected individuals with no two people having the same types of risks. Beyond various health risks, there will be a spectrum of both social and financial risks associated with either returning or not returning that must be considered. None of those disparate risk estimates will be anywhere near as reliable as the cancer risk levels that we have just projected. The cancer risks are just one aspect of the risk/benefit analysis that each evacuee must make. But, for all their imperfections, the cancer risk estimates are the most accurate part of that analysis.

Whether to return to contaminated communities is a hard decision, but all intelligent people are capable of making such a decision about their own health and wellbeing, and they have the right to do so, as long as they have access to credible and intelligible information regarding the risks involved. And it’s actually good that people make their own decisions and not rely on government agencies to make decisions on their behalf because only they, and not the government, know exactly what uniquely personal and individual interests they have at stake.

Timothy J. Jorgensen is author of Strange Glow: The Story of Radiation. He is associate professor of radiation medicine and director of the Health Physics and Radiation Protection Graduate Program at Georgetown University. He lives with his family in Rockville, Maryland.

Five years ago on March 12, following a devastating tsunami, Fukushima Prefecture in Japan experienced the largest release of radioactive materials since the infamous nuclear meltdown in Chernobyl 30 years before. The world, understandably, was braced for the worst. But molecular radiation biologist Tim Jorgensen, author of Strange Glow: The Story of Radiation says this accident was no Chernobyl. The levels measured at Fukushima after the meltdown aren’t much higher than the annual background levels that already existed—a fact that does little to allay fears for many. How much then, do we really know about radiation and its actual dangers? Though radiation is used in everything from x-rays to cell phones, much of the population still has what Jorgensen considers an uninformed aversion to any type of exposure. In this fascinating scientific history, he describes mankind’s extraordinary, often fraught relationship with radiation.

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